This invention relates to RF cable distribution network systems and more particularly to an interface circuit for use with such cable networks, and even more particularity to such a system using co-planer wave guide techniques.
Cable TV networks are well-known and have been used for years to distribute RF signals to TV sets over coaxial cable. Traditionally, this has been a xe2x80x9cbroadcastxe2x80x9d type network for one direction RF transmission. This traditional network is now being converted into a bidirectional network and, at the same time, the data bandwidth is being increased as much as possible. Coupled with this is the requirement that the power be delivered through the cable and that digital data be added/removed from the RF transmission, all without reducing the transmission quality of the RF signal to the TV or other connected devices. This is a lot to ask of an interface circuit, particularly where low cost and low radiation susceptibility are important.
Traditionally, the RF coaxial cable terminates at the TV set. Now it is required to insert a junction box into the cable at some point for each terminating location so as to be able to remove the power and add/remove other signals from the cables.
One problem that needs to be solved is to have minimum RF insertion loss when the junction box is inserted into the existing RF cable. In addition, the return loss of both connectors (the input connection and the connection to the TV set) must be greater than 15 dB. Also, the input power must be removed. In terms of safety, the box must have the ability to withstand lightening which is defined as microsecond spikes with an 80 microsecond half-decay point. The voltage spike levels can reach 6000 volts: Line crosses, when high voltage, such as 600 VAC, can get on RF center conductor, must be handled. Also, there must be some method of suspending service by remote signals applied to the RF line. In addition, because of the power delivery aspect, UL Creepage and Clearance must be met. All of this must be activated while still maintaining low cost manufacturing costs which equates to a low cost manufacturing process.
Typically, what has been done is that there have been different circuits to solve each of those problems. Thus, there are in-line power tap circuits and tuners on printed and circuit boards with connectors thereon which can cut off the RF signal when desired. Usually, these solutions have been add-ons to the tuner and are typically external to the tuner board. To date, with each add-on handling only a subset of the problems. Today there does not exist an integrated tuner solution to the problems discussed above.
The present invention is directed to a system and method which meets all the RF junction box requirements and does so in an economic manner. Our invention relies, in part, on what is called a co-planer wave guide, which is a transmission line technique applied to solve a unique set of problems. The conventional approach would be to use micro strip lines for the input of the tuner. This approach is faulty because of the immediate proximity of many parasitic elements in the RF path. These parasitic elements include walls, relays, capacitors, and other elements which impede the RF performance.
The co-planer wave guide techniques used in one embodiment pulls down the radiation fields and yields much better performance than prior circuits. Lighting protection, line cross protection, AC tap circuitry, relay cut off circuitry, low return and insertion losses, outdoor F-connectors are all achieved within a single housing where an interface is provided to a digital processing circuit.
The foregoing has outlined rather broadly the features and technical advantages of the present invention in order that the detailed description of the invention that follows may be better understood. Additional features and advantages of the invention will be described hereinafter which form the subject of the claims of the invention. It should be appreciated by those skilled in the art that the conception and specific embodiment disclosed may be readily utilized as a basis for modifying or designing other structures for carrying out the same purposes of the present invention. It should also be realized by those skilled in the art that such equivalent constructions do not depart from the spirit and scope of the invention as set forth in the appended claims. The novel features which are believed to be characteristic of the invention, both as to its organization and method of operation, together with further objects and advantages will be better understood from the following description when considered in connection with the accompanying figures. It is to be expressly understood, however, that each of the figures is provided for the purpose of illustration and description only and is not intended as a definition of the limits of the present invention.